Multilayer plastic bottles with mineral filler and foamed layer for improved recyclability

ABSTRACT

Plastic containers exhibiting reduced plastic resin usage, while maintaining a specific gravity of below 1.0, so as to allow their quick and easy separation using floatation techniques during recycling. Within a layer or portion some of the plastic resin of the container body may be replaced with an inorganic mineral filler material, while within another layer or portion of the plastic container, the plastic material (e.g., polyethylene, polypropylene) may be foamed. The fraction of mineral filler material that may be included within the polyethylene may thus be increased beyond that previously possible while maintaining the specific gravity below 1.0, by also foaming a layer or portion of the polymeric material, so as to create voids therein. This allows significantly less resin material to be employed, while maintaining strength characteristics of the plastic container so as to be at least comparable to existing plastic containers not including such mineral filler materials.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of co-pending U.S. patentapplication Ser. No. 14/639,869, filed Mar. 5, 2015.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention is generally related to recyclable plastic bottlesor other containers. In particular, the invention relates to plasticbottles that include a mineral filler material (e.g., an inorganicfiller such as CaCO₃), while providing for higher filler loadings thanpreviously possible, while still providing recyclability.

2. Description of Related Art

Plastic bottles are often made from polyolefin materials. Such plasticmaterials may typically have a specific gravity of from 0.900 to about0.963. Pigments are sometimes added to such materials, which may raisethe specific gravity somewhat. In many communities, such bottles orother containers can be recycled, with polyolefin bottles or othercontainers in the recycling stream being separated from glass, ceramic,polyester, or other materials using floatation separation in afloatation tank. This limits uses of mineral filler materials, whichtypically have densities significantly greater than that of water. Theaddition of too much mineral filler to polyolefin will cause theresulting plastic container to sink in the floatation tank.

Thus, cost reductions and environmental benefits that could be obtaineddue to lower use of petrochemical resin raw materials are limited, whereit is desired to still facilitate floatation separation and recycling ofsuch containers. It would be a benefit in the art to provide the abilityto increase loading of mineral filler materials, while stillfacilitating floatation separation in recycling of such containers.

BRIEF SUMMARY OF THE INVENTION

In an embodiment, the present invention is directed to a plasticcontainer comprising single or multiple layers, which exhibits improvedrecyclability and reduced use of petrochemical resin raw materials. Anexterior first layer may comprise a polyolefin, an interior second layermay comprise a polyolefin, and an interior third layer may also comprisea polyolefin. At least one of the layers may comprise at least one ofpost-consumer or post-industrial recycled material (e.g., regroundpolyethylene, reground polyporpylene). The polyolefin of at least one ofthe layers may be foamed, e.g., a cellular foamed layer including closedcells of a foaming agent within a polyethylene matrix. At least one ofthe layers (e.g., other than the foamed layer) may include a mineralfiller material (e.g., calcium carbonate and/or talc), which providesincreased strength characteristics and reduces the amount of polyolefinneeded.

The mineral filler material may be included in an amount of at least 5%(e.g., at least 7%, or at least 8%) by weight of the layer within whichit is included, while the specific gravity of all of the layers of theplastic container combined together is greater than 0.90 and below 1.0,so that the plastic container floats in water. In an embodiment, themineral filler may be included in an amount that is sufficient so thatthe specific gravity of the plastic container would be greater than 1.0if none of the layers comprised foamed polyolefin. In other words,inclusion of a relatively high fraction of the mineral filler can beoffset (relative to specific gravity) by foaming the polyolefin withinat least one of the layers of the container, so that the specificgravity for the container overall remains less than 1.0, so that thecontainer will float.

Another embodiment is directed to a plastic container including anexterior first layer, the first layer including a polyolefin and acolorant (e.g., TiO₂), an interior second layer comprising a polyolefin,an interior third layer comprising a polyolefin, and an interior fourthlayer comprising a polyolefin. At least one of the layers includes amineral filler material, at least one of the layers comprises at leastone of post-consumer or post-industrial recycled material, and thepolyolefin of at least one of the layers is foamed. The specific gravityof the plastic container as a whole is greater than 0.90 and below 1.0.

Another embodiment is directed to a plastic container comprising acontainer body including at least one layer, with at least one layercomprising a polyolefin, wherein at least a portion of the containerbody comprises foamed a polyolefin. The specific gravity of the plasticcontainer is below 1.0. In addition, the container body includes mineralfiller in an amount that is sufficient so that the specific gravity ofthe plastic container would be greater than 1.0 without the foamed apolyolefin, and has a specific gravity greater than 0.90 and below 1.0.In other words, the inclusion of the foamed a polyolefin offsets some ofthe increase in specific gravity that would otherwise occur due to themineral filler loading, bringing the specific gravity of the plasticcontainer as a whole down below 1.0, so that it floats in water. Such aplastic container may include a single or multiple layers.

Such containers thus may provide a bulk specific gravity for thecontainer as a whole that is below 1.0 (e.g., from greater than 0.90 tobelow 1.0, or from 0.95 to below 1.0, from 0.97 to below 1.0, or from0.98 to below 1.0). This allows the container to float on water, whilepermitting relatively high loading of the mineral filler material (e.g.,which includes a density significantly greater than 1.0 g/cm³) withinone or more of the layers of the plastic container, which relativelyhigher loading (and higher density) can be counterbalanced by therelatively low density of the foamed layer or portions. For example,such containers may include one or more layers having a specific gravitygreater than 1.0, while the bulk specific gravity of the container as awhole remains below 1.0, due to the presence of the foamed layer(s). Inanother embodiment, the mineral filler material may be included in anamount that would drive the specific gravity of the resulting plasticcontainer over 1.0, but for the presence of the foamed layer or portion,which counteracts the specific gravity increase caused by the increasedmineral filler loading, ensuring that the specific gravity for thecontainer remains below 1.0, so that it will float.

Another embodiment is directed to a method of forming a blow-moldedplastic article. Such a method may include providing a polymericmaterial for a parison, the polymeric material comprising a polyolefin(e.g., polyethylene, polypropylene). The polymeric material is conveyedin a downstream direction in an extruder, and a mineral filler materialand a foaming agent (e.g., a physical foaming or blowing agent or achemical foaming agent) are introduced into the extruder (e.g., wherethey may be mixed with the polymeric material). The mineral fillermaterial and foaming agent may be introduced into the extruder and thepolymeric material in any desired order, at any desired location alongthe extruder.

The terms foaming agent and blowing agent may be used interchangeablyherein. The mineral filler may be disposed in at least a portion of thepolymeric material (e.g., it may be in a different portion than thefoaming agent, so that a portion includes the foaming agent, and anotherportion or portions include the mineral filler). The mixture of foamingagent and polymeric material may be subjected to blow molding conditionsto form a cellular foamed blow-molded article. The specific gravity ofthe blow-molded article is greater than 0.90 and below 1.0. Such aplastic blow-molded article may include a single or multiple layers.

Another embodiment is directed to a method of forming a blow-moldedplastic article including multiple layers. Such a method may includeproviding a polymeric material for a multilayer parison, where thepolymeric material includes a polyolefin, each layer including apolyolefin. The polymeric material may be conveyed in a downstreamdirection in an extruder (e.g., with mineral filler and foaming agentbeing added as the polymeric material is conveyed downstream in theextruder). For example, a physical or chemical foaming agent may beintroduced to form a mixture of foaming agent and the polymeric material(e.g., a single phase solution with foaming agent (e.g., supercritical)dissolved in the polymeric material). The mixture may be subjected toconditions (e.g., rapid pressure drop) causing formation of a cellularfoam where tiny cells of the foaming agent are dispersed (e.g., asclosed cells) within a matrix of the polymeric material. Another layerof the blow-molded article comprises a polyolefin and the mineral fillermaterial (e.g., so the filler and foam may be in separate, distinctlayers). As in the embodiments described above, the specific gravity ofall of the layers of the plastic container combined together may begreater than 0.90 and below 1.0.

Further features and advantages of the present invention will becomeapparent to those of ordinary skill in the art in view of the detaileddescription of preferred embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the drawings located in the specification. It isappreciated that these drawings depict only typical embodiments of theinvention and are therefore not to be considered limiting of its scope.The invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a perspective view of an exemplary plastic container accordingto an embodiment of the present invention;

FIG. 2 shows a cut away view through a sidewall of the plastic containerof FIG. 1;

FIG. 3 is a cross-sectional view through an exemplary plastic containersidewall of the present invention, where the plastic container includes3 layers;

FIG. 4 is a cross-sectional view through an exemplary plastic containersidewall of the present invention, where the plastic container includes4 layers;

FIG. 5 is a cross-sectional view through another exemplary plasticcontainer sidewall of the present invention, where the plastic containerincludes 3 layers;

FIG. 6 is a flow chart illustrating an exemplary method for blow-moldinga plastic container according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. DEFINITIONS

Before describing the present invention in detail, it is to beunderstood that this invention is not limited to particularlyexemplified systems or process parameters that may, of course, vary. Itis also to be understood that the terminology used herein is for thepurpose of describing particular embodiments of the invention only, andis not intended to limit the scope of the invention in any manner.

All publications, patents and patent applications cited herein, whethersupra or infra, are hereby incorporated by reference in their entiretyto the same extent as if each individual publication, patent or patentapplication was specifically and individually indicated to beincorporated by reference.

The term “comprising” which is synonymous with “including,”“containing,” or “characterized by,” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps.

The term “consisting essentially of limits the scope of a claim to thespecified materials or steps “and those that do not materially affectthe basic and novel characteristic(s)” of the claimed invention.

The term “consisting of” as used herein, excludes any element, step, oringredient not specified in the claim.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an” and “the” include plural referentsunless the content clearly dictates otherwise. Thus, for example,reference to a “mineral filler material” includes one, two or moremineral filler materials.

The terms “mineral filler” and “mineral” are interchangeable for thepurpose of describing the present invention. The purpose of the mineralfiller may be merely to displace polymer. Alternatively, there arespecialty formulations where the mineral serves may also serve a usefulpurpose that improves the performance of the plastic part (e.g.improving strength, rigidity, durability etc. of the plastic).

Unless otherwise stated, all percentages, ratios, parts, and amountsused and described herein are by weight.

Numbers, percentages, ratios, or other values stated herein may includethat value, and also other values that are about or approximately thestated value, as would be appreciated by one of ordinary skill in theart.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention pertains. Although a number of methodsand materials similar or equivalent to those described herein can beused in the practice of the present invention, the preferred materialsand methods are described herein.

II. INTRODUCTION

The present invention is directed to plastic containers exhibitingreduced plastic resin usage, while maintaining a specific gravity ofbelow 1.0, so as to allow their quick and easy separation using afloatation tank during a recycling process. Thus, the plastic containersexhibit recyclability characteristics comparable to those of existingplastic containers, but also exhibit the ability to reduce usage ofplastic resin raw materials employed in the manufacture of suchcontainers, by inclusion of an inorganic mineral filler material withina matrix of the plastic resin material. The fraction of mineral fillermaterial that may be included within the polyethylene or otherpolyolefin polymeric material may be increased beyond that previouslypossible while maintaining the specific gravity below 1.0, by alsofoaming a layer or portion of the polymeric material, so as to createvoids therein. This allows even less polymeric resin material to beemployed, while maintaining strength and other characteristics of theplastic container so as to be at least comparable to existing plasticcontainers not including such mineral filler materials.

In other words, a portion of the polyolefin resin material may bereplaced with a mineral filler material, and an increase in specificgravity resulting from the loading with the mineral filler may be atleast partially offset by foaming the polyolefin resin material (e.g.,within another layer of the container that does not include mineralfiller material), so that the specific gravity of the container as awhole remains below 1.0.

III. EXEMPLARY PLASTIC CONTAINERS

FIG. 1 shows an exemplary plastic container 100 according to anembodiment of the present invention. The plastic container 100 may beany type or shape of plastic container used to hold any of numerousarticles, such as, but not limited to a canister for holdingdisinfecting wipes, cleaning wipes, or a bottle, box, or other shapedcontainer for holding any desired articles, which container may beformed by blow-molding. Such a plastic container is configured to berecyclable, e.g., formed from a polyolefin material such aspolyethylene. Various polyolefins other than polyethylene, e.g.,polypropylene, may also be suitable for use, although polyethylene maybe particularly suitable for use.

Container 100 may include a container body 102, as well as a containerlid 104 configured to close over the open top 106 of container body 102.As shown, in an embodiment, container body 102 may be generallycylindrically shaped, including a closed bottom 108, and an open top106. An attached or separate lid 104 may be provided for covering opentop 106. Lid 104 may be formed by injection molding, and may comprise asingle layer (e.g., of similar plastic materials, such as polyethylene).FIG. 2 illustrates a cut-away portion through the sidewall of containerbody 102, while FIG. 3 illustrates a more magnified close up view of thesidewall of container body 102, illustrating how container body 102 mayinclude a plurality of layers which together make up the sidewall 110and bottom 112 of container body 102.

Inclusion of a plurality of layers within container body 102 allows foreach layer to include distinct compositional characteristics. Suchcharacteristics may be specifically tailored to provide container body102 with an overall specific gravity that is below 1.0, so thatcontainer body 102 can be easily separated from other articles duringrecycling, while at the same time allowing for a reduction in the amountof polymeric resin (e.g., polyethylene, polypropylene) used in formingcontainer body 102, without necessarily decreasing wall thickness orother dimensional characteristics of container body 102. This may beachieved by replacing a portion of the polymeric resin material (e.g.,polyethylene, polypropylene) with a mineral filler material. Such amineral filler material may be incorporated into the polymeric resinmaterial, reducing the amount of polymeric resin material needed tomanufacture the container body. This may allow for wall thicknesses toactually remain the same, or even increase in thickness.

In an embodiment, the reduction in polymeric resin material may be atleast 5%, at least 7%, at least 8%, at least 10%, at least 12%, at least15%, from 8% to 25%, from 8% to 20%, from 8% to 15%, from 9% to 20%,from 9% to 15%, from 10% to 15%, or other ranges defined between any ofsuch values (e.g., 8% to 12%), while providing strength characteristicsto the container body that are similar to those that would be providedwhere the entire container body were made of the polymeric resin,without any mineral filler material, or a foamed polyolefin.

It will be apparent from the present disclosure that there is a limit tothe amount of mineral filler which may be added to the polymericmaterial of the container body, while still maintaining an overallspecific gravity that is below 1.0, absent other changes to offset theincreased specific gravity caused by the inclusion of the mineral fillermaterial. For example, while polyethylene has a density of about 0.91g/cm³ to about 0.97 g/cm³ (e.g., high density polyethylene (HDPE) havinga density of about 0.94 g/cm³ to about 0.97 g/cm³, depending on specificcharacteristics), the density of a mineral filler material, such ascalcium carbonate (CaCO₃) is about 2.7 g/cm³. Calcium carbonate mineralfiller material may be added as a concentrate thereof, mixed with thepolyethylene or other resin material (e.g., 70%-80% CaCO₃ and 20%-30%polyethylene). As such, it will be appreciated that the density andspecific gravity of such a CaCO₃ concentrate may be somewhat less than2.7.

In any case, it will be apparent that too high a fraction of CaCO₃ willcause the resulting container body to exhibit a specific gravity that isgreater than 1.0, so that the resulting container body will no longerfloat. For example, in HDPE containers that already include a smallfraction of TiO₂ colorant, addition of CaCO₃ would be limited to about5.5% by weight (and a specific gravity of 1.0), even though furtherreductions in resin usage could be achieved with higher mineral fillerloadings.

As such, according to embodiments of the present invention, at least aportion or layer of the container body is also foamed, so as to decreasedensity and specific gravity within the foamed portion. For example, afoaming agent may be introduced into at least a portion of the apolyolefin resin material of the container body, so as to result in amatrix of cellular voids dispersed within the polyolefin material withinthe finished container body. In other words, a portion or layer of thepolyolefin of the container body may be foamed, including tiny cells offoaming agent (e.g., nitrogen, carbon dioxide, or other gas) trappedwithin the polyolefin matrix. Such a foamed portion or layer exhibitsdecreased density and specific gravity, because of the tiny voids wherethe polyolefin material has been displaced. Such a foamed portion orlayer may be employed to offset the increased density and specificgravity associated with the inclusion of a mineral filler materialwithin the polyolefin matrix.

As a result, higher mineral material loadings may be provided, whilemaintaining the overall specific gravity below 1.0, because at least aportion of the increased gravity is offset by foaming a portion or layerof the polyolefin material. In an embodiment, the foamed layer orportion may be kept separate from the mineral filler material, as theinclusion of foaming agent and a mineral filler within the same portionor layer may result in unwanted interactions between such components.For example, the mineral filler may nucleate formation of foamed cells,which may be undesirable. As such, the foamed polyolefin may be presentwithin one layer, while the mineral filler may not be present in thefoamed layer, but may be present within one or more other layers.

Of course, where the container body is formed of only a single layer,both foaming and mineral filler may be present within the same singlelayer. In some embodiments, efforts may be made to still attempt toseparate the foaming agent from the mineral filler material, e.g., byintroducing foaming agent into one side of a single layer, whileintroducing mineral filler material into the opposite side of the singlelayer. Such may result in a structure where the single layer includesdifferently configured portions, effectively providing a pseudo multiplelayer structure. In other embodiments, the foaming agent may beintroduced into the same portion(s) as the mineral filler material ispresent. As mentioned, it may be preferred to maintain separationbetween the foaming agent and the mineral filler material.

FIG. 3 shows a close up of a cross-section of an exemplary sidewall 110,illustrating an example of the present invention including three layers.For example, exterior first layer 114 may form the exposed exteriorsurface of sidewall 110. An interior second layer 116, and an interiorthird layer 118 may also be provided. At least one of the layers 114-118may differ from another of the layers in compositional characteristics.For example, although each layer may comprise a polyolefin, one or moreadditional components, such as a foaming agent, a mineral fillermaterial, a colorant, etc. may be present within some of the layers. Forexample, a mineral filler material such as calcium carbonate may beadded to one or more of the layers. At least one of the layers maycomprise a polyolefin into which a foaming agent has been introduced, sothat the polyolefin is foamed. The inclusion of the mineral fillermaterial increases the specific gravity of the container 100, whilefoamed polyolefin serves to decrease the specific gravity of thecontainer. Thus, inclusion of the foamed polyolefin serves to offset atleast some of the increase in specific gravity provided by the mineralfiller material loaded within one or more layers.

Because of the offset provided by the foamed polyolefin, the fraction ofmineral filler material loaded within the container 100 may be greaterthan would otherwise be possible while maintaining the specific gravityof the container at a value that is below 1.0. For example, the mineralfiller material may be present at a value of more than 5%, more than 7%,more than 8%, more than 10%, more than 15%, or more than 20% by weight.Such percentages may be relative to the layer in which the mineralfiller material is included, or relative to the plastic container bodyas a whole.

Relatively higher mineral filler loading fractions allow forcorrespondingly greater reductions in the amount of polyolefin used inmanufacture of the container. For example, the reduction in polyolefinresin usage may be at least 5%, at least 7%, at least 8%, at least 10%,at least 12%, at least 15%, or a range defined between any two suchpoints (e.g., 8% to 12%).

In the embodiment shown in FIG. 3, exterior layer 114 may comprise apolyethylene matrix material and a colorant, such as titanium dioxide(TiO₂). Such a colorant may serve to opacify layer 114 (and sidewall110), and/or provide a color (e.g., white) thereto. Any desired colorantmay be included within layer 114 (or another layer). Although TiO₂ maybe included primarily as a colorant, it has a density significantlyhigher than that of the polyethylene resin matrix material, increasingspecific gravity of the container, similar to the effect caused byinclusion of a mineral filler material, such as calcium carbonate. Forexample, such a TiO₂ colorant may be provided as a concentrate, e.g., inwhich 45% by weight of the concentrate is actually TiO₂ while theremaining 55% may be polyethylene. In an embodiment, such included TiO₂may be considered to form a portion of the mineral filler material,although another mineral filler material such as calcium carbonate maytypically also be present (e.g., in an amount higher than the TiO₂colorant).

Internal layer 116 may be sandwiched between exterior layer 114 andlayer 118. Layer 116 may include a mineral filler material dispersedwithin the polyethylene matrix thereof. Such mineral filler may beincluded in an amount of at least 5% by weight of the layer in which itis included, or by weight of the container body as a whole. Higherpercentages as described herein may be provided (e.g., more than 7%,more than 8%, more than 10%, more than 15%, or more than 20% by weight).

Third layer 118 may form the interior surface of container body 102. Aswith other layers 114 and 116, layer 118 may comprise a polyethylenematrix. A foaming agent (e.g., either chemical or physical) may beincorporated into the polyethylene resin from which layer 118 is formed,forming tiny cells within the matrix of layer 118. As a result, once thepolyethylene resin layer 118 cools, the result is a layer 118 thatcomprises foamed polyethylene, including tiny cells or voids 120 presentwithin the matrix of polyethylene. Cells or voids 120 include a very lowdensity (e.g., they may be filled with the gaseous foaming agent). Theinclusion of such a foamed polyethylene provides layer 118 with aspecific gravity that is significantly lower than the specific gravityof the polyethylene material itself. The lower specific gravity offoamed layer 118 offsets at least some of the increase in specificgravity provided by the inclusion of the mineral filler material presentwithin one or more layers. In an embodiment, the foamed polyethylene andthe mineral filler material are not present within the same layer (i.e.,one layer is foamed, while one or more other layers include the mineralfiller material).

FIG. 4 illustrates another embodiment of a sidewall 210, including 4layers 214, 216, 218, and 220, each including polyethylene. Exteriorlayer 214 may provide the outer exposed exterior surface of sidewall210. A colorant may be included within exterior layer 214 (or any of thelayers). A mineral filler may be present within one or more of thelayers. The polyethylene of one or more of the layers may be foamed(e.g., cells or voids 222 of layer 220).

As shown in FIGS. 3 and 4, in an embodiment, it may be beneficial thatthe foamed polyethylene layer be the innermost layer of the sidewall(i.e., forming the interior surface of container body 102). Such aconfiguration may maximize the cooling rate of the container body afterblow molding, as heat is removed from the polyethylene resin materialthrough the outermost layer of the bottle. In another embodiment, thefoamed layer may be sandwiched between two adjacent layers, as seen inFIG. 5. This may be helpful as the interface or outer edge surfaces ofthe foamed layer may be rough, or somewhat uneven, due to the presenceof cells or voids 120, which intersect the outer edge surface orinterface. Such a sandwiched configuration may serve to fill over orcover any roughness resulting from such cells or voids at the outer edgesurface of layer 118 (i.e., the interface between layer 118 and theadjacent sandwiching layers 114 and 116) so that neither the exteriorsurface nor an interior surface is roughened.

Foaming of one or more of the layers will result in a thicker layer thanwould otherwise be provided, all else being equal, except for thefoaming. In other words, foaming a given layer will cause that layer tothicken and expand as it is foamed, as it accommodates the expansion ofthe bubbles of foaming agent grown therein. Such increased thickness mayalso serve to increase the overall thickness of the entire sidewall,which increases top loading strength of the wall at a given bottleweight, which advantageously provides for increased crush resistance.

For example, in an embodiment, a foamed layer may have a thickness fromabout 2 to about 15 mils, from about 15 to about 30 mils, or about 30 toabout 90 mils. In an embodiment, the increase in thickness of the foamedlayer may be from about 1 percent to about 10 percent, from about 10 toabout 30 percent, or about 30 to about 90 percent. In an embodiment, thefoamed layer may be the thickest of all the layers of the containersidewall. In an embodiment, the foamed layer may be 0 percent to about50 percent thicker, 50 percent to about 200 percent thicker, or 200percent to about 900 percent thicker than the next thickest layer of thesidewall.

The foaming agent may be included in an amount to provide a void volumeof at least about 1%, at least 3%, at least 5%, at least about 10%, atleast about 15%, from 15% to about 30%, from about 15% to about 25%,from 1% to 20%, from 10% to 20%, or any other ranges defined betweenendpoint values described above. Such percentages may be relative to thefoamed layer, or relative to the container body as a whole.

A portion of the polyethylene resin material employed in manufacture ofthe bottle may be recycled, e.g., from post-industrial and/orpost-consumer sources. In an embodiment, the recycled material ispost-industrial material that may be reground (e.g., from off cuts andother scrap portions, rejected bottles etc.) and used in the formationof one or more of the layers. In another embodiment, post-consumerrecycled materials, or combinations of post-consumer and postindustrialrecycled materials may be employed. For example, a regrind ratio may beup to about 0.8 (i.e., 8 pounds of reground HDPE for every 10 pounds ofvirgin HDPE resin), from 0.2 to 0.7, or from 0.3 to 0.6. Stated anotherway, in some embodiments, the recycled materials may comprise from about10% to 20%, from about 20% to about 40%, or from 40 to about 60% byweight of a given layer.

FIG. 6 describes a method S10 for forming a blow-molded plasticcontainer. For example, at S12 a polymeric material for a parison isprovided. The polymeric material may comprise a polyolefin having adensity of less than 1.0 (e.g., polyethylene, polypropylene). Thepolymeric material may be conveyed in a downstream direction in anextruder (e.g., a blow-molding machine). A mineral filler material and afoaming agent may be introduced into the extruder in any order, and atany desired location along the extruder. The foaming agent and thepolymeric material form a mixture. At S14, the mixture of the foamingagent and the polymeric material may be subjected to blow-moldingconditions to form a cellular foamed blow-molded layer or portion of ablow-molded article. For example, the mixture may be subjected toconditions (e.g., rapid pressure drop) causing formation of a cellularfoam where tiny cells of the foaming agent are dispersed (e.g., asclosed cells) within a matrix of the polymeric material, and thesidewalls may be blown out towards the edges of the mold of theblow-molding machine. The blow-molded article may be removed from theblow-molding machine, and allowed to cool. At S16, the conditions aresuch that the specific gravity of the blow-molded article is greaterthan 0.90, and below 1.0.

For example, as described herein, the specific gravity of theblow-molded article (e.g., a container) including both a mineral fillermaterial and a foaming agent dispersed within a polymeric matrixmaterial (e.g., such as polyethylene, polypropylene) may be from 0.90 tobelow 1.0, from 0.95 to below 1.0, from 0.97 to below 1.0, or from 0.98to below 1.0.

As described herein, the foaming agent introduced within the polymerresin melt may be maintained in a separate layer or portion from themineral filler material (e.g., the layer(s) of the polymer that arefoamed with the foaming agent may not include any significant fractionof the mineral filler material).

A small amount of a nucleating agent may be included with the foamingagent in the foamed layer, to nucleate formation of the desired tinycells. Small amounts of talc or other nucleating agents may be employed.In some embodiments, the nucleating agent may be the same as the mineralfiller material, although typically if included as a nucleating agent,its loading will be significantly lower than where included for purposesof acting as a filler. For example, such a nucleating agent may bepresent at 7% or less, less than 6%, less than 5%, less than 4%, lessthan 3%, less than 2%, or less than 1% by weight. Even where the samematerial is employed elsewhere in the container body as a mineral fillermaterial, it will be apparent that its inclusion may be limited in thefoamed layer (e.g., less than 5%), while it may be included in muchhigher fractions in other, non-foamed layers. Where a chemical foamingagent is employed (e.g., sodium bicarbonate and citric acid), noseparate nucleating agent is needed, as such a foaming agent isself-nucleating. Nucleating agents may be included when employingphysical blowing agents, such as nitrogen or carbon dioxide.

Polyethylene is an example of a particularly suitable polymeric resinmaterial employed in the manufacture of the presently describedblow-molded plastic containers. It will be appreciated that thepolymeric material employed may advantageously have a specific gravitythat is below 1.0, so as to allow the container formed therefrom tofloat. Relatively lower specific gravity values for a given polymericresin material allows introduction of the mineral filler material (e.g.,which includes a significantly higher specific gravity than thepolymeric resin material) within the polymeric resin material atrelatively higher weight fractions, while still maintaining the specificgravity of the manufactured container at a value that is below 1.0, soas to allow its separation from other materials within a floatation tankduring or in preparation for recycling. Table 1 below shows specificgravity for some such plastic materials.

TABLE 1 Plastic Specific Gravity Low Density Polyethylene (LDPE)0.91-0.93 High Density Polyethylene (HDPE) 0.94-0.97 Polypropylene (PP)0.90-0.91 Polystyrene (PS) 1.04-1.07 Polyvinylchloride (PVC) 1.35-1.45Acrylonitrile Butadiene Styrene (ABS) 0.99-1.10 Polyester 1.38-1.39Polycarbonate 1.2 Nylon 66 1.13-1.15 Polytetrafluoroethylene (TEFLON)2.1-2.2

Examples of potentially suitable polymeric resin materials includevarious grades of polyethylene (e.g., LDPE, HDPE), as well aspolypropylene. It will be appreciated that blends of a plurality ofpolymeric resin materials may also be employed, in some embodiments. Insome embodiments, it may be possible to even include polymeric resinmaterials having a specific gravity equal to or greater than 1.0 withina blend of resins, where the overall resin blend includes a specificgravity of less than 1.0. In an embodiment, HDPE may be particularlypreferred.

Calcium carbonate may be preferred for use as the mineral fillermaterial, although it will be apparent that other inorganic mineralfiller materials may alternatively be employed. For example, talc mayalso represent a suitable mineral filler material. The specific gravityvalue of calcium carbonate is about 2.7, while that of talc is about2.75. For example, the mineral filler material may typically have aspecific gravity from about 1.5 to about 3.0 or from about 2.5 to about3.0.

IV. EXAMPLES AND TESTING DATA Example 1

Trial samples of 1 liter round bottles were manufactured as describedbelow. For each example, high density polyethylene from EQUISTAR wasemployed as the polymeric resin material. Some of the samples includedfoamed polyethylene, while others included foam and calcium carbonate asa mineral filler material. Each of the trial samples included 3 layers(A, B, and C), where layer A formed the exposed exterior surface of thebottle, layer C formed the interior surface of the bottle, and layer Bwas sandwiched between layers A and C (similar to the structures shownin FIGS. 3 and 5).

Within those examples that included a foamed polyethylene layer, thefoam was generated using a chemical foaming agent of sodium bicarbonateand citric acid, available from CLARIANT CORP., located in Charlotte,N.C. It will be appreciated that other bases and acids (e.g., organicacids) may be employed. Physical foaming agents, such as carbon dioxideand/or nitrogen may alternatively be employed (e.g., injected into theappropriate extruder).

Example 1-1

Example 1-1 was a clear (i.e., no colorant) control, includingpolyethylene without any foamed polyethylene, and without any mineralfiller material. The weight of the example was 53.9 g, and it had aspecific gravity of 0.954.

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2260 18 TiO₂ — — — CaCO₃ — — — Foam — — — HDPE 100% 100% 100%

Example 1-2

Example 1-2 was a white (i.e., TiO₂ colorant) control, includingpolyethylene without any foamed polyethylene, and without any mineralfiller material. The weight of the example was 54.3 g, and it had aspecific gravity of 0.959.

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  7% — — CaCO₃ — — — Foam — — — HDPE 93% 100% 100%

Example 1-3

Example 1-3 was a foamed bottle, without any colorant in any of thelayers, to better visually ascertain the foam structure. None of thelayers included any mineral filler material. The weight of the examplewas 49.7 g, and it had a specific gravity of 0.901. Based on the cost ofmaterials involved, this example included a cost reduction as comparedto the control (Example 1-2) of 4.1%. As the cost reduction is due todecreased use of the polyethylene resin, the weight or volume reductionin polyethylene use is similar (i.e., about 4%).

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2452 24 TiO₂ — — — CaCO₃ — — — Foam (HY1622) —  3% — HDPE 100% 97% 100%

Example 1-4

Example 1-4 was a foamed bottle, and included colorant in one of thelayers. None of the layers included any mineral filler material. Theweight of the example was 47.4 g, and it had a specific gravity of0.894. Based on the cost of materials involved, this example included acost reduction as compared to the control (Example 1-2) of 9.2%. As thecost reduction is due to decreased use of the polyethylene resin, theweight or volume reduction in polyethylene use is similar (i.e., about9%). The foaming agent employed in this example was more concentrated oractive than that employed in Example 1-3, increasing the amount of foam(i.e., increasing the overall volume occupied by the foam cells).

Component or Characteristic Layer A Layer B Layer C Layer % by Weight19.5 61 19.5 TiO₂ concentrate —  0.9% — CaCO₃ — — — Foam (J-001) —   2%— HDPE 100% 97.1% 100%

Example 1-5

Example 1-5 was a foamed bottle, and included colorant in one of thelayers at a level providing similar opacity as the control Example 1-2.Because of the presence of the foamed layer, which contributes to theopaque white color, less TiO₂ colorant is needed to achieve a similardegree of opacity. None of the layers included any mineral fillermaterial. The weight of the example was 47.8 g, and it had a specificgravity of 0.895. Based on the cost of materials involved, this exampleincluded a cost reduction as compared to the control (Example 1-2) of8.6%. As the cost reduction is due to decreased use of the polyethyleneresin, the weight or volume reduction in polyethylene use is similar(about 9%). The foaming agent employed in this example was the same asthat employed in Example 1-4.

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  2.3% — — CaCO₃ — — — Foam (J-001) —  2% — HDPE97.7% 98% 100%

Example 1-6

Example 1-6 was a foamed bottle similar to Example 1-5, but included ahigher concentration of the foaming agent, which further thickens thebottle wall. The weight of the example was 48.0 g, and it had a specificgravity of 0.899. Based on the cost of materials involved, this exampleincluded a cost reduction as compared to the control (Example 1-2) of5.5%. As the cost reduction is due to decreased use of the polyethyleneresin, the weight or volume reduction in polyethylene use is similar(about 6%).

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2356 22 TiO₂ concentrate  2.3% — — CaCO₃ — — — Foam (J-001) —  3% — HDPE97.7% 97% 100%

Example 1-7

Example 1-7 was a foamed bottle also including calcium carbonate mineralfiller material, and a colorant in at least one of the layers. Theweight of the example was 49.0 g, and it had a specific gravity of0.933. Based on the cost of materials involved, this example included acost reduction as compared to the control (Example 1-2) of 12.6%. As thecost reduction is due to decreased use of the polyethylene resin, theweight or volume reduction in polyethylene use is similar (about 13%).In Example 1-7, without the foamed layer, the weighted average specificgravity of the bottle would be greater than 1.0 (i.e., about 1.01). TheCaCO₃ mineral filler material employed in this example was a concentrateincluding 80% calcite, with a specific gravity of 1.96. The TiO₂colorant material employed in this example was similarly a concentrate(e.g., 45% TiO₂), with a specific gravity value of 1.52. The mineralfiller concentrate comprised 10.6% (8.48% CaCO₃) by weight of the bottleas a whole. Including the TiO₂ colorant, the mineral filler and coloranttogether (because both have a similar effect on specific gravity)comprised about 8.8% by weight of the bottle as a whole.

Component or Characteristic Layer A Layer B Layer C Layer % by Weight18.5 63 18.5 TiO₂ concentrate  2.3% — — CaCO₃ concentrate 28.5% — 28.5%Foam (J-001) —  3% — HDPE 69.2% 97% 71.5%

Example 1-8

Example 1-8 was a foamed bottle also including calcium carbonate mineralfiller material, a colorant in at least one of the layers, and recycledpolyethylene material within at least one of the layers. The weight ofthe example was 49.4 g, and it had a specific gravity of 0.945. Based onthe cost of materials involved, this example included a cost reductionas compared to the control (Example 1-2) of 12.3%. As the cost reductionis due to decreased use of the polyethylene resin, the weight or volumereduction in polyethylene use is similar (about 12%).

As in Example 1-7, the CaCO₃ mineral filler concentrate materialemployed in this example was 80% calcite, with a specific gravity of1.96. The TiO₂ colorant material employed in this example was similarlya concentrate (e.g., 45% TiO₂), with a specific gravity value of 1.52.The mineral filler concentrate comprised 9.4% by weight of the bottle asa whole. Including the TiO₂ colorant, the mineral filler and coloranttogether (because both have a similar effect on specific gravity)comprised about 10.2% by weight of the bottle as a whole. Without thefoamed layer, the specific gravity of the bottle would be greater than1.0 (i.e., about 1.02).Al1 of the TiO₂ colorant used in the Examples was45% TiO₂ by weight. Recycled polyethylene in the form of post-industrialwaste material (e.g., reground polyethylene material from previousbottle production) was reground and put into the bottle, in layer B. Theinclusion of such recycled post-industrial material was compatible withfoaming of layer B, such that the strength characteristics of theresulting bottle were similar to those of Example 1-7, which did notinclude such recycled polyethylene material.

Component or Characteristic Layer A Layer B Layer C Layer % by Weight18.5 63 18.5 TiO₂  2.3% 0.9%  — CaCO₃  20% 7% 20% Foam (J-001) — 3% —HDPE 77.7% 89.1%   80%

Example 1-8 includes both CaCO₃ filler and foaming within the same layer(e.g., layer B). While possible in some embodiments, a configurationsimilar to Example 1-7 may be preferred over inclusion of mineral fillermaterial and foaming within the same layer, as it was observed uponmicroscopic examination that the cell walls in the foamed layerruptured, which results in a roughened texture, as compared to Example1-7, where the foamed layer does not include any mineral filler (orinorganic mineral colorant). In Example 1-7, the cells rather werebelieved to start out round, and to become elongated as the bottle wasblown out during blow-molding, but that the cells did not rupture, butremained closed, generally intact. The practical effects of anyroughened texture at the interface of a layer that is both foamed andincludes mineral formulated with a filler material may be minimized bysandwiching such a layer between layers which do not include bothfoaming and a mineral filler, as in Example 1-8.

Example 2

Containers such as those manufactured according to Example 1 above maybe employed to hold disinfecting wipes, or other contents, as shown inFIG. 1. An important characteristic of such canister shaped containersis “Dynamic Vertical Load”, where a lid (e.g., injection molded fromsimilar plastic materials) is placed on the container, and the containerwith lid is slowly crushed. Force versus displacement curves may begenerated from the data generated during such a test. A relativelyhigher peak load force value is desirable, indicating the containerexhibits relatively higher resistance to being crushed. Such acharacteristic is important as pallets of such containers are typicallystacked in warehouses, trucks, and stores during storage andtransportation. Too low of a dynamic vertical load value correlates tocontainers at the bottom of such stacks of pallets becoming crushed, andunusable. Data from the Dynamic Vertical Load test is presented in Table2, below, for several tested examples, including some of those ofExample 1.

TABLE 2 Peak Displace- Load @ Load @ Load @ Load ment @ 0.05 0.25 0.125Weight Sample (lbf) Peak Load in-lbf in-lbf in-lbf (grams) Control 1-168.00 0.17 43.61 56.72 61.73 53.95 Control 1-2 68.38 0.17 43.83 57.1862.01 53.91 Control 2-1 67.61 0.17 42.56 56.24 61.32 54.69 Control 2-268.68 0.17 44.38 58.52 61.15 54.40 3-1 79.63 0.22 41.65 78.27 58.7250.13 3-2 84.93 0.22 43.64 83.56 63.04 52.37 4-2 76.54 0.22 36.16 75.1556.88 48.97 5-1 64.93 0.22 25.84 61.58 51.47 47.40 5-2 78.39 0.24 34.4477.93 54.69 49.16 6-1 77.53 0.23 37.00 76.53 56.67 49.27 6-2 73.28 0.2133.71 70.57 57.03 49.00 7-1 69.74 0.22 31.97 67.79 53.45 48.90 7-2 66.880.21 29.28 63.12 52.16 48.80 8-1 54.80 0.17 26.51 40.68 50.57 47.43 8-269.25 0.17 35.43 56.33 61.24 49.76

As shown, control samples 1 and 2 (Control 1-1, Control 1-2 and Control2-1 and Control 2-2), which correspond to Examples 1-1 and 1-2 ofExample 1, together averaged a peak maximum load of 68.2 lbf at a bottleweight of 54.2 g. Samples 7-1 and 7-2 (corresponding to Example 1-7)averaged a peak maximum load of 68.3 lbf at a bottle weight of 48.9 g.In other words, while exhibiting a reduction in bottle weight of about10%, Example 1-7 was able to achieve a peak maximum load approximatelyequal to that of the control. Furthermore, the reduction in polyethyleneresin usage is approximately equal to the bottle weight reduction, asabout 9% of the polyethylene resin is replaced by the mineral fillermaterial. Such lower petrochemical use (i.e., reduced polyethylene resinuse) is a major environmental sustainability and cost reduction benefit.There are two reasons for resin use reduction. First, the drop in weightoccurs because we choose to put less material in the bottle (i.e. weslow down the extruder but keep the rate of bottle making the same). Thesecond reduction in resin use occurs because we replace resin withmineral. The drop in petrochemical use is the combination of the drop inweight of the bottle plus the percent of resin replaced by mineral.

In an embodiment, the inventive containers exhibit peak load values thatare similar to or greater than those of existing containers, formedwithout foam and without mineral filler materials (other than TiO₂ forcoloring). For example, the peak load value of these one liter foamedand mineral filled plastic containers may be at least 50 lbf, at least55 lbf, at least 60 lbf, from 50 lbf to about 100 lbf, from 55 lbf to 90lbf, or from 60 lbf to 75 lbf.

In addition to exhibiting excellent peak load value (i.e., crushstrength) characteristics, the foamed and mineral filled plasticcontainers may exhibit reduced petrochemical (e.g., polyethylene) usageof at least 5%, at least 7%, at least 8%, at least 9%, at least 10%,from 8% to 25%, from 8% to 20%, from 8% to 15%, from 9% to 20%, from 9%to 15%, or from 10% to 15%.

Example 3

Example 3 describes additional hypothetical proposed multi-layer trialsamples similar to those of Example 1. For each example, high densitypolyethylene from EQUISTAR is employed as the polymeric resin material.Some of the samples include foamed polyethylene, while others includedfoam and calcium carbonate as a mineral filler material. Each of thetrial samples includes 3 layers (A, B, and C), where layer A forms theexposed exterior surface of the bottle, layer C forms the interiorsurface of the bottle, and layer B is sandwiched between layers A and C(e.g., similar to the structure of FIGS. 3 and 5).

Within those examples that include a foamed polyethylene layer, the foammay be generated using a chemical foaming agent of sodium bicarbonateand citric acid, available from CLARIANT CORP., located in Charlotte,NC. It will be appreciated that other bases and acids (e.g., organicacids) may alternatively be employed. Physical foaming agents or blowingagents, such as carbon dioxide and/or nitrogen may alternatively beemployed (e.g., injected into the appropriate extruder).

Example 3-1

Example 3-1 is a white colored (i.e., including TiO₂ colorant inexterior layer A) control, including polyethylene without any foamedpolyethylene, and without any mineral filler material. The regrind ratioof the HDPE material in layer B is 0.6 (i.e., 6 lbs of reground HDPEmaterial is included for every 10 lbs of virgin HDPE material).

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  7% — — CaCO₃ — — — Foam — — — HDPE 93% 100% 100%

Example 3-2

Example 3-2 is a white colored (i.e., including TiO₂ colorant inexterior layer A) test sample, including polyethylene with a foamedpolyethylene internal layer, and without any mineral filler material.The regrind ratio of the HDPE material in layer B is 0.6 (i.e., 6 lbs ofreground HDPE material is included for every 10 lbs of virgin HDPEmaterial). The inclusion of foaming within layer B allows for areduction in the TiO₂ content in layer A, while providing a similardegree of opacity to the bottle (similar to Example 1-5).

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  3% — — CaCO₃ — — — Foam —  3.3% — HDPE 97% 96.7%100%

Example 3-3

Example 3-3 is a white colored (i.e., including TiO₂ colorant inexterior layer A) test sample, including polyethylene with a foamedpolyethylene internal layer, and which also includes mineral fillermaterial within layers A and C. No reground HDPE material is included inany of the layers. The inclusion of foaming within layer B allows for areduction in the TiO₂ content in layer A, while providing a similardegree of opacity to the bottle (similar to Example 3-2). The CaCO₃concentrate is 70% CaCO₃ (e.g., with the 30% balance being HDPE), sothat the CaCO₃ content within layers A and C is 24.5%, and the bottle asa whole includes a CaCO₃ content of 9.8% by weight. The TiO₂ is aconcentrate including 45% TiO₂ (with the remainder being HDPE) so thatthe bottle has a TiO₂ content of 0.27%. Content of CaCO₃ plus TiO₂ is10.07%. The bottle has a specific gravity of greater than 0.9 and lessthan 1.0.

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  3% — — CaCO₃ concentrate 35% — 35% Foam —  3.3%— HDPE 62% 96.7% 65%

Example 3-4

Example 3-4 is a white colored (i.e., including TiO₂ colorant inexterior layer A) test sample, including polyethylene with a foamedpolyethylene internal layer, and which also includes mineral fillermaterial within layers A and C. The regrind ratio of the HDPE materialin layer B may be up to 0.6 (i.e., 6 lbs of reground HDPE material isincluded for every 10 lbs of virgin HDPE material). The inclusion offoaming within layer B allows for a reduction in the TiO₂ content inlayer A, while providing a similar degree of opacity to the bottle(similar to Example 3-2). The CaCO₃ concentrate is 70% CaCO₃ (e.g., withthe 30% balance being HDPE), so that the CaCO₃ content within layers Aand C is 24.5%, and the bottle as a whole includes a CaCO₃ content of9.8% by weight. The TiO₂ is a concentrate including 45% TiO₂ (with theremainder being HDPE) so that the bottle has a TiO₂ content of 0.27%.Content of CaCO₃ plus TiO₂ is 10.07%. The bottle has a specific gravityof greater than 0.9 and less than 1.0.

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  3% — — CaCO₃ concentrate 35% — 35% Foam —  3.3%— HDPE 62% 96.7% 65%

Example 3-5

Example 3-5 is a white colored (i.e., including TiO₂ colorant inexterior layer A) control sample, including polyethylene with a foamedpolyethylene internal layer C, and which does not include mineral fillermaterial within any of the layers. No recycled reground HDPE material isincluded in any of the layers. The inclusion of foaming within layer C(which forms the interior surface of the bottle) allows for a reductionin the TiO₂ content in layer A, while providing a similar degree ofopacity to the bottle (similar to Example 3-2).

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  3% — — CaCO₃ — — — Foam — —  3.3% HDPE 97% 100%96.7%

Example 3-6

Example 3-6 is a white colored (i.e., including TiO₂ colorant inexterior layer A) test sample, including polyethylene with a foamedpolyethylene internal layer C, and which includes mineral fillermaterial within layers A and B. The regrind ratio of the HDPE materialin layer B may be up to 0.6 (i.e., 6 lbs of reground HDPE material isincluded for every 10 lbs of virgin HDPE material). The inclusion offoaming within layer C (which forms the interior surface of the bottle)allows for a reduction in the TiO₂ content in layer A, while providing asimilar degree of opacity to the bottle (similar to Example 3-2). TheCaCO₃ concentrate is 70% CaCO₃ (e.g., with the 30% balance being HDPE),so that the CaCO₃ content within layers A and C is 12.6%, and the bottleas a whole includes a CaCO₃ content of 10.08% by weight. The TiO₂ is aconcentrate including 45% TiO₂ (with the remainder being HDPE) so thatthe bottle has a TiO₂ content of 0.27% (10.35% for CaCO₃ plus TiO₂).

Component or Characteristic Layer A Layer B Layer C Layer % by Weight 2060 20 TiO₂ concentrate  3% — — CaCO₃ concentrate 18% 18% — Foam — — 3.3% HDPE 79% 82% 96.7%

Without departing from the spirit and scope of this invention, one ofordinary skill can make various changes and modifications to theinvention to adapt it to various usages and conditions. As such, thesechanges and modifications are properly, equitably, and intended to be,within the full range of equivalence of the following claims.

1. A method of forming a blow-molded plastic article, the methodcomprising: (a) providing a polymeric material for a parison, thepolymeric material comprising a polyolefin; (b) conveying the polymericmaterial in a downstream direction in an extruder; (c) introducing amineral filler material into the extruder to be mixed with at least aportion of the polymeric material; and (d) introducing a foaming agentinto the extruder to form a mixture of foaming agent and the polymericmaterial; and (e) subjecting the mixture of foaming agent and polymericmaterial to blow-molding conditions to form a cellular foamedblow-molded article; and (f) wherein the specific gravity of theblow-molded article is greater than 0.90 and below 1.0.
 2. The method ofclaim 1, wherein the polymeric material comprises polyethylene.
 3. Themethod of claim 1, wherein the foaming agent is a physical foamingagent.
 4. The method of claim 1, wherein the foaming agent is a physicalfoaming agent selected from the group consisting of carbon dioxide,nitrogen, and combinations thereof.
 5. The method of claim 1, whereinthe foaming agent is a chemical foaming agent.
 6. The method of claim 1,wherein the cellular blow-molded article is a container.
 7. The methodof claim 1, wherein the polymeric material further comprises a colorant.8. The method of claim 6, wherein the container comprises two or morelayers.
 9. The method of claim 8, wherein at least one of the layers hasa different thickness than at least one other layer.
 10. The method ofclaim 8, wherein at least one layer of the container has a void volumeof at least about 10%.
 11. The method of claim 8, wherein at least onelayer of the container has a void volume of from about 15% to about 30%.12. A method of forming a blow-molded plastic article including multiplelayers, the method comprising: (a) providing a polymeric material for amultilayer parison, the polymeric material comprising a polyolefin; (b)conveying the polymeric material in a downstream direction in anextruder; (c) introducing a mineral filler material into at least one ofthe layers comprising polyolefin so that at least one of the layers ofthe parison comprises the mineral filler material and polyolefin, atleast one of the layers differing in composition from another layer ofthe parison; (c) introducing a foaming agent into at least one of thelayers comprising polyolefin to form a mixture of foaming agent and thepolymeric material; and (d) subjecting the mixture of foaming agent andpolymeric material to blow-molding conditions to form a cellular foamedblow-molded layer, another layer of the blow-molded article comprisingpolyolefin and the mineral filler material; and (e) wherein the specificgravity of the blow-molded article including multiple layers is greaterthan 0.90 and below 1.0.
 13. The method of claim 12, wherein the layerincluding polyolefin and the mineral filler material has a specificgravity above 1.0, and the cellular foamed layer has a specific gravitybelow 1.0, so that the blow-molded article including all layers combinedhas a specific gravity below 1.0.
 14. The method of claim 12, whereinthe polyolefin comprises polyethylene.
 15. The method of claim 12,wherein the foaming agent is a physical foaming agent.
 16. The method ofclaim 12, wherein the foaming agent is a physical foaming agent selectedfrom the group consisting of carbon dioxide, nitrogen, and combinationsthereof.
 17. The method of claim 12, wherein the foaming agent is achemical foaming agent.
 18. The method of claim 12, wherein thepolymeric material further comprises a colorant.
 19. The method of claim12, wherein at least one of the layers has a different void volume thanat least one other layer.
 20. The method of claim 12, wherein at leastone of the layers has a different thickness than at least one otherlayer.